Field of the Disclosure
This disclosure relates generally to welding methods and apparatus used in welding. More particularly, the disclosure relates to the manufacturing of flow meters that measure parameters related to the flow of a liquid or a gas. Still more particularly, it relates to methods and apparatus for installing and sealing transducers in ultrasonic flow meters.
Background Information
Hydrocarbons, in both liquid and gas phases, are transported from place to place via pipelines, ships, and other containers. When the fluid changes hands, the event is called a “custody transfer.” Custody transfers occur while the hydrocarbons are passed between one or more systems of pipelines, and while being loaded or off-loaded from a ship, for example. During custody transfers, it is particularly desirable to know accurately the amount of fluid flowing in a stream. Even where custody transfer is not taking place, measurement accuracy is desirable for record keeping and engineering evaluations, and in these situations, ultrasonic flow meters are commonly used.
An ultrasonic flow meter typically includes a meter body through which a fluid flows and two or more transducer assemblies, each secured inside a dedicated port in the flow meter body. The flow meter body may also be called a spool piece. To seal the fluid within the flow meter, a conventional transducer housing is threadingly secured within each port in the spool piece, and a transducer is sealed within the housing. Thus, the spool piece and transducers and transducer housings create a sealed container and pressure boundary that contains the fluid that is flowing through the meter.
The ports and transducers are arranged and positioned in pairs in the meter, and such that the transducers of the pair face each other from opposite sides of the fluid-carrying bore of the spool piece. When coupled within the transducer housings, the piezoelectric elements of the transducers are adjacent to the inner surface of the fluid-carrying bore. The transducers transmit and receive acoustic signals back-and-forth across the fluid stream. Each transducer is coupled to external electronics that alternately generate and interpret the electrical signals sent to and received from the piezoelectric elements of the transducers.
A mechanical seal is typically used to seal the transducer housing into the threaded port in the spool piece. A common mechanical seal for this application is a face-seal which includes a seal material compressed between two opposing metal surfaces. Where such seals are used in systems conveying liquid natural gas (LNG), the seals must operate at a temperature near minus 170 degrees Celsius and are commonly made from Teflon®. At such extreme temperatures, the seal material may lack the required resiliency. Further, the two metal surfaces contacting the seal material must have a very fine surface finish, requiring a hand-polishing process to achieve the necessary smoothness. Thus, the use of mechanical seals for installation of a transducer housing in a meter through which LNG is conveyed involves manufacturing complications and potential modes of failure. Therefore, it would be beneficial to implement a method of coupling and sealing a transducer housing to a meter body that would prevent hydrocarbon leakage without the use of threads and a removable seal material.